New route to 2-cyanobenzimidazoles

Article abstract of DOI:10.1016/S0040-4020(98)00521-3

N-Monosubstituted 1,2-diaminobenzenes 4 (R = Me, Ph, PhCH₂, and 3,4- Me₂C₆H₃CH₂) react with 4,5-dichloro-1,2,3-dithiazolium chloride 1 in dichloromethane at room temperature to give the corresponding 2- cyanobenzimidazoles 6. If pyridine is added at the beginning of the reaction, the intermediate imino-1,2,3-dithiazoles 5 can be isolated. Upon thermolysis, most of the imines 5 give the 2-cyanobenzimidazoles 6 in fair to good yields. 1.2-Diaminobenzene can be converted in high yield into the mono-imine 5i or the bis-imine 12, R = H; thermolysis of 5i gives 2-cyanobenzimidazole in high yield. Conversion of 5 into 6 involves the loss of both sulfur atoms and with the N-phenylimino derivative 5b singlet diatomic sulfur, S₂, has been intercepted with norbornene and with 2.3-diphenylbutadiene to give the expected cycloadducts 7 and 8.